Lines

Lines lead the eye to points or between points within an image.  The conscious use of lines can be used to enhance the prominence of the subject, to tell the subject's story (what the subject[s] is[are] doing/thinking), or help create 3-dimensional depth to the image in general.  The nature of the lines can also be used to create a mood.
 
 
 

Line Psychology

The very nature of the lines in a photograph have a general psychological effect on how the image is perceived.  This effect seems to universally cut across diverse cultural boundaries and is deeply rooted in our psyche.

Straight Lines

Straight lines exude hardness, power and strength.  In terms of gender they are thought of as primarily masculine.  In the photograph of the dam, note all the straight lines.  Indeed, all the lines defining the dam are straight.  These, combined with the rough textured surface, combine to give the subject a sense of strength, solidity, hardness and power.

Curved Lines

Curved lines signal softness, tenderness, shyness and calm.  In gender they are a sign of femininity.  Note the contrast in mood between this photograph and the previous, both taken in the same locale on the same day.  This one has near zero straight lines.  Two significant lines, a stream bed and road, are curved.  The horizon and tree lines appear curved also giving the scene a sense of serenity and tranquility.
 

Perspective

An object, or portion of an object, will appear smaller as the distance from the its viewer increases.  Photographs capture this same effect called "perspective."  This effect reveals the object or scene's visible depth.  Because a photograph is a flat image, we unconsciously use intuition and life experience seeing objects of similar shape to perceive perspective.  The bridge photograph demonstrates this.  The arches, railing and light standards all get smaller as the eye travels from the right side of the image to the left.  Our intuition tells us bridges are level, light standards are the same size, rivers are level (going across them) and the arches are likely all the same size.  The horizontal lines among them are parallel and equally spaced in reality.  However, from our POV (point of view) they are not.  Therefore the part of the bridge in the image's right side is closer than the part of the bridge on the left side.  We need not see much, if any, of the far shoreline to come to this conclusion subconsciously and automatically.  This is reinforced by the size of everything that is part of the bridge, including the footings just above the water, getting smaller at the same rate.  A look at the first and second photographs in this section also show perspective clearly.  The first with the railing and the second with the dam structure itself.

Vanishing Points

When a perspective POV shows an object's parallel lines getting closer together, the vanishing point is where the lines converge and represents theoretically an infinite distance away from the observer.  Obviously something an infinite distance away cannot be seen in reality, much less captured in a photograph.  In this image, the vanishing point is behind the rounded top structure far down the street.  Note how nearly all the perspective lines, including the tops of the light standards and a weak one formed by corners of buildings all lead to the same point.  All images with some form of perspective have one or more vanishing points.  Whether there is only one, or more than one depends on the perspective.

Leading Lines

Leading lines are perspective lines that lead the viewer to the subject or an element of the subject.  There are two elements in the subject of this photograph:  the dam which dominates the image and the person looking at the dam who is quite small by comparison.  There is some color contrast, but it is the leading lines (also perspective lines) of the railing, benches, and bottom edge of the corrugated wall that lead the eye to the person.  Without them, the person looking at the dam would not be as prominent in this image because of small size and lack of strong color contrast.  The eye is lead by these lines toward a vanishing point behind the dam through where the person is standing.

Hidden Lines

Hidden lines are those not created by the shapes in the image, but by the position and orientation of subject elements.  In the photograph of the waterfall, there is one of the most common hidden leading lines from the girl to the waterfall because that is where she is looking.  With a living subject element, the viewer's eye is naturally drawn to where the subject is looking if it is elsewhere in the image.  This can be used to capture uniqe effects that help draw attention to the main subject element, or tell the story about the subject and interaction among subject elements.  Although the technical aspect of lighting in the photograph of the card game is not the best, the direction two of the participants are looking tells a powerful story.  There is little doubt whose turn it is next and that there is some suspense as to what he will do.  A direction of motion can also create a hidden leading line.  If it is obvious a subject element is moving within the image, the eye will also naturally be drawn to where that element is headed.  In the night image of the man walking on the bridge (me with the camera on tripod using the self-timer), it is obvious he is walking toward the bright lights in the center of the city.  Note the direction is also the same as the perspective lines of the bridge with an apparent destination at the vanishing point in the bright lights in the distance.  In this image it combines several line and perspective properties working together to strengthen the perception of the viewer.  We know where he is headed leaving some mystery as to why he is going there and doing so that late at night with the rest of the locale deserted by traffic and people.

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